1. Field of the Invention
The present invention relates to an apparatus for pulling a molding ring off a neck of a concrete tubular workpiece formed by the molding ring, which comprises two clamping jaws positioned diametrically opposite each other with respect to a vertical axis of the tubular workpiece, the clamping jaws overlapping the molding ring from above and engaging the workpiece below the molding ring, a supporting structure displaceably supporting the clamping jaws, and a lifting device arranged on the supporting structure for two pull-off catches arranged diametrically opposite each other with respect to the molding ring, the pull-off catches subtending an undercut of the molding ring.
2. Description of the Prior Art
Molding rings are used to form centering necks of tubular concrete workpieces and remain on the molded necks while the workpiece is removed from its mold. To enable the molding ring to be pulled off the neck of the at least partially hardened concrete workpiece without impairing the manufacturing tolerances or damaging the tubular workpiece, Austrian patent No. 397,939 proposes to hold the workpiece with clamping pliers positioned diametrically opposite each other with respect to a vertical axis of the workpiece and gripping the molding ring from above, and to pull the molding ring off the firmly held workpiece. A lifting device for pull-off catches is mounted on a supporting structure for the clamping pliers, and the pull-off catches are moved radially inwardly towards the molding ring until they subtend undercuts of the molding ring provided for this purpose. The lifting device then lifts the pull-off catches with the molding ring from the firmly held workpiece. Since the clamping pliers as well as the pull-off catches are freely displaceable, an adjustment drive connecting the pull-off catches for engaging the catches with the molding ring, the molding ring is pulled off the workpiece under favorable load conditions. However, the pull-off catches, which are part of an auxiliary frame connected to the supporting structure by the lifting device, must be angularly offset with respect to the clamping pliers, which requires a structurally determined minimum diameter of the tubular workpiece.
It is the primary object of this invention to provide an apparatus of the above-indicated type, with which molding rings may be advantageously pulled off the necks of workpieces of smaller as well as larger diameters.
The invention accomplishes this and other objects with an apparatus of the first-described structure, wherein the clamping jaws and pull-off catches are arranged on carriages which are adjustable in opposite directions along coaxial guides.
With this arrangement, the pull-off catches need not be angularly offet with respect to the clamping pliers but may be coaxial therewith on the carriages whereon they are mounted, which carriages are diametrically opposite each other with respect to the vertical axis of the workpiece and are adjustable in opposite directions along radial guides. Such a pull-off apparatus has no limits for the inner diameter of the workpiece since the workpiece is gripped only from the outside by the diametrically opposed clamping jaws.
To avoid bending loads on the workpiece due to the clamping jaws engaging the outside of the workpiece, the clamping jaws are advantageously arranged to engage the tubular workpiece from the outside and are part of clamping pliers gripping the inside and the outside of the tubular workpiece. In this case, the smallest inner diameter of the workpiece is determined by the structure of the clamping pliers whose inner jaws together must be inserted in the bore of the workpiece.
A simple construction is obtained when the clamping pliers comprise double-armed clamping levers linked to the carriages, clamping drives engaging one end of each clamping lever and the clamping jaws being carried by the opposite ends of the clamping levers. In this case, symmetrical load conditions are obtained if the clamping levers comprise two parts pivoted to opposite sides of a carriage body, the clamping jaws being pivotally positioned between the clamping lever parts to obtain a planar engagement of the clamping jaws with the workpiece and a load-free holding grip of the workpiece. This requires the outer clamping levers of the two clamping pliers to be guided outwardly past the pull-off catches to avoid their interfering with each other. To meet this requirement while obtaining favorable levering conditions, the carriage body may have two projections at respective sides of the molding ring, the clamping lever parts being pivoted to the projections.
To enable the lifting forces required to pull the molding ring off the neck of the workpiece to be held to a minimum, it may be necessary under some conditions to loosen the molding ring on the neck. For this purpose, hammers may be provided for the pull-off catches, the hammers being mounted on the carriages at a radial distance from, and outwardly of, the pull-off catches. When desired, the hammers may hit the pull-off catched from below and thus assist the loosening of the molding ring from the neck.
While this is not absolutely necessary, it is useful if the lifting device has a lifting unit associated with each carriage for each pull-off catch since the pull-off catches are arranged on two carriages. Simple constructional conditions are achieved in this case with an apparatus wherein a carrier for each pull-off catch is mounted on the carriages, each carrier being adjustable by a respective one of the lifting units along a lifting guide, and each pull-off catch being pivotally mounted on the carrier for pivoting about an axis extending tangentially to the vertical axis of the workpiece. The pivotal mounting of the pull-off catches on the carriers offers a space-saving adjustability of the catches, which may be lifted for pulling the molding ring off after they have subtended the undercuts of the molding ring. Each lifting guide advantageously comprises a sliding block inserted in a guide recess of a carriage body, and each carrier comprises two carrier jaws connected to the sliding blocks, extending along the sides of the carriage body and projecting upwardly from the carriage body. The lifting unit may be arranged between the two carrier jaws forming the carrier for a respective one of the pull-off catches and is supported, on the one hand, by the carriage body and, on the other hand, engages the clamping jaws. This produces a compact, symmetrical structure combining a favorable use of space with good load conditions.